Photoflash lamp

ABSTRACT

A photoflash lamp in which the combustible metal within the oxygen-filled lamp envelope comprises a quantity of shredded foil, such as zirconium or hafnium, for providing a source of actinic light, and a much smaller quantity of an oxygenscavenging metal, such as coarse strands of aluminum or magnesium, for quickly and effectively reducing the internal pressure in the lamp to below one atmosphere following actinic combustion. The rapid reduction in pressure after usable light emission significantly improves the containment capability of the lamp. The proportionate quantity and nature of the oxygenscavenging metal are selected to provide the desired pressure reducing function with essentially no effect on photometric output.

United States Patent [191 Shaffer im 3,822,109 [45] July 2,1974

[ PHOTOFLASH LAMP John W. Shaffer, Williamsport Pa.

[73] Assignee: GTE Sylvania Incorporated,

' Danvers, Mass.

[22] Filed: Nov. 21, 1972 [2]] Appl. No.: 308,313

[75] Inventor:

[ 52] US. Cl. 431/93 511 Int. Cl. F2 lk 5/02 Field of Search 431/95, 94, 93

[56] References Cited 1 UNITED STATES PATENTS 2,142.372' 1/1939 Pipkin Ct Bl 431/95 2,334 l55 1 11/1943 Oram i i l 431/95 3.301674 2/1967 Anderson 431/95 1491)}55 1/1970 Buzalski .1 431/95 3,630,650 12/1971 FOREIGN PATENTSOR APPLICATIONS 303,021 8/1965 Netherlands ..431/95 Kaufmann et al. 431/95 Prim'ary Examiner-Carroll B. Dority, Jr. Assistant Examiner-Harold Joyce I Attorney, Agent, or Firm-Edward .1. Coleman [57] i ABSTRACT A photoflash lamp in which the combustiblemetal within the oxygen-filled lamp enwelope'comprises a fquantity of shredded foil, such as zirconium or hafnium, for providing a source of actinic light; and a muchsmaller quantity of an oxygen-scavenging metal, such as coarse strands of aluminum or magnesium, for quickly and effectively reducing the internal pressure in thelllamp to below one atmosphere following actinic combustion. The rapid reduction in pressureafter usable light emission significantly improves the containment capability of the lamp. The proportionate quantity and nature of the oxygen-scavenging, metal are selected to provide the desiredpressure reducing function with essentially no effect on photometric output.

10 Claims, 3 Drawing Figures INTERNAL LAMP PRESSURE (Cm Hg.) N x IOO PATENTEBJUL 21914 38221109 SHEET 2 [IF 2 I l I I IOO (M l LLl SECONDS) TIME v ,1 PHOTOFLASH LAMP BACKGROUND OF THE INVENTION filamentary combustible material, such as shredded zirconium or hafnium foil, and a combustion-supporting gas, such as oxygen. In subminiature lamps the glass envelope typically has a tubular shape and an internal volume of less than one cubic centimeter. In lamps intended for battery operated flash systems, the envelope also contains an electrical ignition system comprising a fine tungsten filament supported on a pair of lead-in wires having a quantity of ignition paste on the inner ends thereof adjacent to the filament. This type lamp is'operated by the passage of electric current through the leadin wires. In the case of percussive-type photoflash lamps, such as described in US. Pat. No. 3,535,063, a mechanical primer is sealed in one end of the lamp envelope. The primer may comprise a metal tube extending from the lamp envelope and a charge of fulminating material on a wire supported in the tube. Operation of the percussive photoflash lamps is initiated by an impact onto the tube to cause deflagration of the fulminating material up through the tube to ignite the combustible disposed in the lamp envelope.

In order to reinforce the glass envelope and improve its containment capability, it has been common practice to coat the lamp envelope with a protective lacquer, such as cellulose acetate.

The oxygen within the lamp is initially present at an elevated pressure, e.g., 8 atmospheres. During lamp flashing, the oxygen is heated and the internal pressure rises to a peak value approximately 60 per cent higher than the initial value. Another event that takes place during flashing of the lamp is impingement of molten globules of metals and oxides from the actinic combustion onto the inner glass surface. This localized thermal shock and stressing causes the glass to spall (or flake off small chips from the inner surface), crack, or grossly disintegrate. It is the function of the cellulose acetate lacquer coating to support the cracked or broken glass vessel and to generally maintainthe integrity of the flashlamp during reaction.

The internal pressure, as stated previously, reaches a high peak value. This occurs early in the flash cycle (e.g., l3-20 milliseconds). From that time on, as the reaction consumes oxygen, the internal pressure within the lamp gradually declines, so that by a time of 160 milliseconds, the internal presusre is approximately one atmosphere. lt is seen, therefore, that the potential severity of lamp rupture is a time dependent function as it is determined by the difference between lamp internal pressure and atmospheric pressure. It is also apparent that the later in the flash cycle glass cracking or failure occurs, the better will be the containment characteristics of the lamp. It is for this reason that various methods of delaying crack time by reinforcing or altering envelope structure have been actively investigated by various flashlamp manufacturers.

Both contamination and the additive effect of manufacturing tolerances, however, can give rise to occasional lamps with higher internal pressure excursions than normal. Excess oxygen, when present, gives rise to abnormally high internal pressures late in the flash cycle. Accordingly, it has been standard practice in the flashlamp industry to load lamps with excess shredded combustible above the stoichiometric ratio to more completely consume any excess oxygen in the lamp envelope. When using a relatively expensive combustible fill, such as shreded zirconium or hafnium foil, however, such a practice is economically disadvantageous. Further, the combustion of zirconium and hafnium is limited by the rate of diffusion of oxygen through an oxide film on the burning globules. As a result they do not burn to completion so as to use all available oxygen.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to economically provide a photoflash lamp having an improved containment capability.

Another object of the invention is to provide economical means for substantially improving the containment of subminiature, high pressure flashlamps by reducing the internal pressure to a value below one atmosphere after the useful light output has been generated therein, said means having essentially no effect on photometric output.

.These and other objects, advantages and features are attained, in accordance with the principles of this invention, by adding to the lamp a slow igniting, fast burning, oxygen-scavenging metal. More specifically, I have discovered that the internal oxygen pressure in subminiature flashlamps can be quickly and effectively reduced to below one atmosphere following actinic combustion by incorporation of a coarse, more slowly ignited secondary combustible, such as aluminum, magnesium, or alloys thereof. The location and area/- volume ratio of the oxygen-scavenging metal are selected to appropriately delay its ignition until the primary combustible has generated a useful light output, and the proportion by weight of the metal is selected to limit its effect to rapid oxygen-scavenging following actinic combustion, but without having any materially contributing effect on usable light output.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more fully described hereinafter in conjunction with the accompanying drawings, in which:

FIG. 1 is an enlarged elevation of an electrically ignitable photoflash lamp containing an oxygen-scavenging metal in accordance with the invention;

FIG. 2 is an enlarged sectional elevation of a percussive-type photoflash lamp containing an oxygenscavenging metal in accordance with the invention; and,

FIG. 3 shows plots of internal lamp pressure versus time for two similar lamps, one with and one without an oxygen scavenger in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENT The teachings of the present invention are applicable to either percussive or electrically ignited photoflash lamps of a wide variety of sizes and shapes; however, the invention is particularly advantageous as applied to flash lamps having tubular shaped envelopes with a volume of less than 1 cubic centimeter (cc.). Accordingly,

FIGS. 1 and 2 respectively illustrate electrically ignited and percussive-type photoflash lamps embodying the principles of the invention.

Referring to FIG. 1, the electrically ignitable lamp comprises an hermetically sealed lamp envelope 2 of glass tubing having a press 4 defining one end thereof and an exhaust tip 6 defining the other end thereof. Supported by the press 4 is an ignition means comprising a pair of lead-in wires 8 and 10 extending through and sealed into the press. A filament l2 spans the inner ends of the lead-in wires, and beads of primer l4 and 16 are located'on the inner ends of the lead-in wires 8 and 10, respectively, at their junction with the filament. Typically, the lamp envelope 2 has an internal diameter of less than one half inch, and an internal volume of less than 1 cc., although the present invention is equally suitable for application to larger lamp sizes. The exterior surface of the glass envelope is covered with a protective coating such as cellulose acetate lacquer. A combustion-supporting gas, such as oxygen, and a filamentary combustible material 18, such as shredded zirconium or hafnium foil, are disposed within the lamp envelope. Typically, the combustion-supporting gas fill is at a pressure extending one atmosphere, with the more recent 'subminiature lamp types having oxygen fill pressures of up to several atmospheres. In accordance with the invention, the lamp envelope also contains a quantity of oxygen-scavenging metal 19, such as aluminum or magnesium, in the form of a bundle of relatively coarse wire located near the top of envelope 2, as viewed in FIG. 1, above the much finer strands of combustible 18. v

The pe'rcussive-photoflash lamp illustrated in FIG. 2 comprises a length of glass tubing defining an hermetically sealed lamp envelope 22 constricted at one end to define an exhaust tip 24 and shaped to define a seal 26 about a primer 28 at the other end thereof. The primer 28 comprises a metal tube 30, a wire anvil 32, and a charge of fulminating material 34. A combustible 36, such a filamentary zirconium or hafnium, and a combustion-supporting gas, such as oxygen, are disposed within the lamp envelope, with the fill gas being at a pressure of greater than one atmosphere. The exterior surface of the glass envelope is covered with a protective coating such as cellulose acetate lacquer. In accordance with the invention, the lamp also contains a quantity of oxygen scavenging metal 37, such as aluminum or magnesium, in the form of a bundle of relatively coarse wire located near the top of envelope 22, as viewed in FIG. 2, above the much finer strands of combustible 36.

The wire anvil 32 is centered within the tube 30 and is held in place by a circumferential indenture 38 of the tube 30 which loops over the head 40, or other suitable protuberance, at the lower extremity of the wire anvil. Additional means, such as lobes 42 on wire anvil 32 for example, may also be used in stabilizing the wire anvil, supporting it substantially coaxial within the primer tube 30 and insuring clearance between the fulminating material 34 and the inside wall of tube 30. A refractory bead 44 is fused to the wire anvil 32 just above the inner mouth of the primer tube 30 to eliminate tube 30 burn-through and function as a deflector to deflect and control the ejection of hot gases from the fulminating material in the primer. The lamp of FIG. 2 is also typically a subminiature type having envelope dimensions similar to those described with respect to FIG. 1.

Although the lamp of FIG. 1 is electrically ignited, usually from a battery source, and the lamp of FIG. 2 is percussion-ignitable, the lamps are similar in that in each the ignition means is attached to one end of the lamp envelope and disposed in operative relationship with respect to the filamentary combustible material 18 or 36. More specifically, the igniter filament 12 of the flash lamp in FIG. 1 is incandesced electrically by current passing through the metal filament support leads 8 and 10, whereupon the incandescent filament l2 ignites the beads of primer l4 and 16 which in turn ignite the combustible 18 disposed within the lamp envelope. Operation of the percussive-type lamp of FIG. 2 is initiated by an impact onto tube to cause deflagration of the fulminating material 34 up through the tube 30 to ignite the combustible 36 disposed within the lamp envelope. The invention is also applicable to other types of electrically ignited lamps, such as those having spark gap or primer bridge ignition structures.

Referring briefly to FIG. 3, curve A represents the variation of internal lamp pressure over a period of time from the point of ignition to about 160 milliseconds after ignition for a flashlamp containing only shredded zirconium foil. It will be noted that the tail of the pressure curve declines in a relatively gradual manner and does not fall below one atmosphere (76 cm. Hg.) until about I50 milliseconds have elapsed. According to the present invention, an oxygen-scavenging metal is added to the lamp to substantially reduce this tail pressure to below one atmosphere immediately afterthe usable light emission, but without materially affecting the usuable photometric output. To provide this effect, the oxygen scavenger is selected to be metal of such a configuration that it ignites more slowly than the primary combustible 18 or 36, so as to delay its ignition toward the tail protion of the pressure curve, but which upon ignition vaporizes and burns very rapidly so as to quickly consume, or scavenge, the oxygen and thereby rapidly reduce internal lamp pressure. Coarse wire or shreds of relatively volatile metals, such as aluminum or magnesium, have been found to be quite suitable as scavengers. Once ignited, these metals vaporize and burn rapidly until the available oxygen is consumed. This is in direct contrast to the burning behavior of low volatility metals, such as zirconium or hafnium, which burn as molten globules with oxide crusts. Curve B represents the internal lamp pressure function for a lamp of the same type associated with curve A but with the addition of a small amount of coarse aluminium shreds. It will be noted that after reaching a peak nearly as high as that of curve A, which coincides with the combustion peak, pressure curve B abruptly drops to below one atmosphere at a point about 46 milliseconds after ignition. The lamp, of course, cannot burst once its internal pressure falls below atmospheric, independent of any consideration of glass failure or lacquer softening. Since glass failure generally occurs fairly late in the flash cycle, therefore, it is apparent that the use of an oxygen scavenger provides a significant improvement in lamp containment.

To achieve the desired oxygen-scavenging function but avoid affecting the peak, duration, or rise and fall times of the light output characteristic of the flashlamp, I control the proportions by weight of the fine and coarse combustibles contained in the lamp. For lamps in which the light generating combustible 18 or 36 is present (from stoichiometric oxygen balance to 20 percent in excess thereof) in quantities ranging from about 2 to 6 mgs./cc-atmosphere of fill pressure, the scavenger metal should be added in quantities ranging from about 0.25 to 1.0 mg./cc-atmosphere.

Timing of the action of the oxygen-scavenging charge can be approximately determined by its area/volume ratio and its location within the lamp. For example in the case of shreds or wire, the area/volume ratio can be controlled by cross-section. I have found that suitable results can be achieved by using scavenger-metal configurations having an area/volume ratio (in square inches per cubic inches of material) ranging from about 300 to 1,600. This compares with typical area/volume ratios of 3,500 to 4,000 for the conventional shredded foil combustible 18 or 36 employed in'flashlamps. With the hot shredsbelow. That is, I prefer to locate the scavenger-metal at the opposite end of the lamp from that to which the ignition means is attached, with the filamentary, light-generating combustible disposed therebetween. I

In one typical embodiment of the invention, electrically ignitable flashlamps, having an internal envelope volume of 0.78 cc., were initially loaded with mgs. of shredded zirconium foil comprising 0.286 inch strands having a cross-section of 0.95 X L3 mils. The zirconium shreds were to serve as the light-generating combustible for determining the usable photometric output of the lamps. After insertion of the zirconium shreds, 3 mgs. of coarse aluminum shreds were blown into each lamp to function as an oxygen scavenger. The strands of aluminum were 4 inches long and had a cross-section of 2 X 4 mils. The finished lamps contained an initial oxygen fill pressure of 650 cm. Hg. Upon ignition, these lamps exhibited the internal pressure vs. time characteristic represented'by curve B of V FIG. 3. The oxygen-scavenging action of the aluminum is dramatically illustrated by the sharp reduction in tail pressure as compared to curve A, which was plottedfor a group of control lamps. The control lamps were identical to the test lamps except that they did not contain aluminum. That is, the control lamps were electrically ignitable, had an internal envelope volume of 0.78 cc., contained 30 mgs. of zirconium shreds measuring 0.95 X 1.3 mils 0.286 inch, and having an initial oxygen fill pressure of 650 cm. Hg.

The inventive principle disclosed herein is potentially applicable to any flashlamp that uses metal combustibles that burn as oxide-coated molten globules. It is contemplated that the metals yttrium, thorium, lanthanum, and uranium would burn in much the same manner as do zirconium and hafnium, and that flashlamps using these metals as combustibles would be similarly benefited with oxygen scavengers as described herein.

may be placed in the lamp either loosely or with suit- -6 able attachment as, for example, to the lead-in wires or anvil of electrical or percussive type lamps, respectively.

In summary, a feature of the invention is the provision of a metallic memberor device within a flashlamp for the purpose of reacting with oxygen that remains after light output is substantially complete. A particular feature is the provision of miniaturized flashlamps that offer enhanced containment by virtue of a rapid drop of internal pressure to below atmospheric values after usable light emission therefrom.

Although the invention hasbeein described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention. In any event, the weight proportions and the area/volume ratios of the respective combustibles must be suitable forproviding the desired oxygen scavenging function without materially affecting usable light output. This'is to be distinguished from the use of coarse and fine combustibles in U.S. Pat. No. 2,334,155 of J. H. Cram, and the use of magnesium and zirconium in U.S. Pat. No.-3,490,855 ofB. T. Buzalski. Oram describes a flashlamp in which the combustible fill consistspartly of heavy aluminum wire having a relatively slow rate of combustion and partly of relatively fine aluminum wire having a high rate of combustion. The proportions by weight are given as heavy Wire 60-80 percent and fine wire 10-15 percent. The purpose of Orams combustible arrangement is to affect the light output'characteristic, namely, tov provide a flash of light characterizedby a rapid rise time and prolonged uniform duration for focal plane cameras. In contrast, my flashlamp employs two different combustible materials with a totally different and reversed'weight proportion to accomplish a different purpose, namely, oxygenscavengingwithout effecting light output. Buzalski employs laminated strands of combustible (e.g., zirconium-magnesium-zirconium) to affect light output, namely, to provide a higher level of illumination while retaining a rapid rise time and short duration light output characteristic. Again, this purpose is totally different from the objects of my invention and is reflected by the unrelated weight proportions and area/volume ratios. Further, when a laminate strand is ignited, all components tend to burn at the same time, thereforeno delayed igntion of the magnesium layer could take place.

What I claim is: a

l. A photoflash lamp comprising:

, an hermetically sealed, light-transmitting envelope;

a combustion-supporting gas in said envelope;

a quantity of strands of a first combustible metal material located in said envelope for providing a source of actinic light; asignificantly smaller quantity of strips by weight of a second and different combustible metal material comprising one or more distinct pieces of metal structurally indepen dent of said first combustible material located at one end of said envelope for rapidlyscavenging said combustion-supporting gas substantially subsequent to actinic combustion of said first combustible material and without materially affecting the usable light output therefrom, said second combustible material having a substantially lower surface area/volume ratio and being more slowly ignitable but faster burning than said firstcombustible material; and

ignition means attached to one end of said envelope and disposed in operative relationship with respect to said first combustible material.

2. A lamp according to claim 1 wherein the quantity of said first combustiblein said envelope ranges from about 2 to 6 mgs./cc-atmosphere, and the quantity of said second combustible in said envelope ranges from about 0.25 to 1.0 mg./cc-atmosphere.

3. A lamp according to claim 1 wherein said second combustible material has an area/volume ratio in square inches per cubic inches of material which ranges from about 300 to 1,600. 7

4. A lamp according to claim 1 wherein said first combustible comprises a metal which burns as a molten globule with an oxide crust, and'said second combustible is a metal which exhibits a relatively delayed ignition but a higher volatility once ignited, whereupon the ignited second combustible tends to vaporize and rapidly and completely consume the combustionsupporting gas in said envelope.

5. A lamp according to claim 4 wherein said second combustible comprises aluminum, magnesium, or alloys thereof.

6. A lamp according to claim 4 wherein said first combustible comprises zirconium or hafnium.

7. A lamp according to claim 1 wherein said quantity of second combustible material is located at the opposite end of said lamp envelope from said end to which said ignition means is attached, with said quantity of first combustible material substantially disposed therebetween. I

8. A lamp according to claim 1 wherein the internal volume of said envelope .is less than about one cubic centimeter, said combustion-supporting gas in said envelope is oxygen at an initial fill pressure exceeding one atmosphere, and said first combustible material is filamentary.

9. A lamp according to claim 8 wherein said first combustible comprises a metal which burns as a molten globule with an oxide crust, said second-combustible is a metal which is relatively slow igniting but tends to vaporize once ignited, said first combustible has an area/- volume ratio of from about 3,500 to 4,000 and is present in said envelope in a quantity of about 2 to 6 mgs./cc-atmosphere, and said second combustible has an area/volume ratio of from about 300 to 1,600 and is present in said envelope in a quantity of about 0.25 to 1.0 mg./cc-atmosphere.

10. A lamp according to claim 9 wherein said'first combustible is shredded zirconium foiLand said sec- 0nd combustible is aluminum wire located at the opposite end of said envelope from said end to which said ignition means is attached, with said shredded zirconium foil substantially disposed therebet'ween. 

2. A lamp according to claim 1 wherein the quantity of said first combustible in said envelope ranges from about 2 to 6 mgs./cc-atmosphere, and the quantity of said second combustible in said envelope ranges from about 0.25 to 1.0 mg./cc-atmosphere.
 3. A lamp according to claim 1 wherein said second combustible material has an area/volume ratio in square inches per cubic inches of material which ranges from about 300 to 1,600.
 4. A lamp according to claim 1 wherein said first combustible comprises a metal which burns as a molten globule with an oxide crust, and said second combustible is a metal which exhibits a relatively delayed ignition but a higher volatility once ignited, whereupon the ignited second combustible tends to vaporize and rapidly and completely consume the combustion-supporting gas in said envelope.
 5. A lamp according to claim 4 wherein said second combustible comprises aluminum, magnesium, or alloys thereof.
 6. A lamp according to claim 4 wherein said first combustible comprises zirconium or hafnium.
 7. A lamp according to claim 1 wherein said quantity of second combustible material is located at the opposite end of said lamp envelope from said end to which said ignition means is attached, with said quantity of first combustible material substantially disposed therebetween.
 8. A lamp according to claim 1 wherein the internal volume of said envelope is less than about one cubic centimeter, said combustion-supporting gas in said envelope is oxygen at an initial fill pressure exceeding one atmosphere, and said first combustible material is filamentary.
 9. A lamp according to claim 8 wherein said first combustible comprises a metal which burns as a molten globule with an oxide crust, said second combustible is a metal which is relatively slow igniting but tends to vaporize once ignited, said first combustible has an area/volume ratio of from about 3,500 to 4,000 and is present in said envelope in a quantity of about 2 to 6 mgs./cc-atmosphere, and said second combustible has an area/volume ratio of from about 300 to 1,600 and is present in said envelope in a quantity of about 0.25 to 1.0 mg./cc-atmosphere.
 10. A lamp according to claim 9 wherein said first combustible is shredded zirconium foil, and said second combustible is aluminum wire located at the opposite end of said envelope from said end to which said ignition means is attached, with said shredded zirconium foil substantially disposed therebetween. 